The VideoLAN Forums

Greetings VLCers,

We're a post-production and distribution house and have been running into an interesting issue that I bet you all could help with in short order. We use VLC on Mac OSX 10.9.x to spot check .mpg and .mxf files before delivery because Quicktime, well, sucks.

Here's the problem:

On VLC 2.0.1, multichannel audio plays back fine but video playback is stuttery (not real time). On any version after 2.0.1 (recent testing has included 2.1.0 and 2.1.5), video playback is perfect but audio playback is garbled and filled with static. I'm guessing this has something to do with a change in the way audio is decoded between 2.0.1 and newer versions.

The audio is plain-old linear PCM and is being played back through stereo headphones - no receiver or multichannel output involved.

Here is the MediaInfo for an example file:

General
ID : 1000 (0x3E8)
Complete name : /Volumes/Transcoding/Transcoding/04_OUTPUTS/Google/NBC_EDTV_FEATURE_HD_10CH_FR_EN_DA000528639_16X9_178_2398_DIGITAL_ARCHIVE.mpg
Format : MPEG-TS
File size : 77.6 GiB
Duration : 2h 3mn
Overall bit rate mode : Constant
Overall bit rate : 90.3 Mbps

Video
ID : 481 (0x1E1)
Menu ID : 2 (0x2)
Format : MPEG Video
Format version : Version 2
Format profile : 4:2:2@High
Format settings, BVOP : Yes
Format settings, Matrix : Default
Format settings, GOP : M=3, N=10
Codec ID : 2
Duration : 2h 3mn
Bit rate : 78.1 Mbps
Maximum bit rate : 80.0 Mbps
Width : 1 920 pixels
Height : 1 080 pixels
Display aspect ratio : 16:9
Frame rate : 23.976 fps
Color space : YUV
Chroma subsampling : 4:2:2
Bit depth : 8 bits
Scan type : Progressive
Compression mode : Lossy
Bits/(Pixel*Frame) : 1.570
Time code of first frame : 00:00:00:00
Time code source : Group of pictures header
Stream size : 67.1 GiB (86%)

Audio
ID : 1002 (0x3EA)
Menu ID : 2 (0x2)
Format : PCM
Format settings, Endianness : Little
Muxing mode : AES3
Codec ID : 6
Duration : 2h 3mn
Bit rate mode : Constant
Bit rate : 6 144 Kbps
Encoded bit rate : 7 680 Kbps
Channel(s) : 8 channels
Sampling rate : 48.0 KHz
Bit depth : 16 bits
Stream size : 5.28 GiB (7%)


Any help or advice you can provide would be greatly appreciated. I can also provide as many more details as you need, just let me know.

Thanks!

Hi,

Bitrate is quite high on your file, so I assume you have a fast storage? Maybe it already helps if you increase VLCs caching.

What would be helpful is a VLC log to see what is happening. You can open the messages window before playback, and then save the log after starting playback. Interesting as well is the audio output method. I assume you have some sort of external soundcard for that? Finally, you can test the latest VLC 2.2 nightly build.

Hi dfuhrmann,

Thanks for the fast response!

Yes we do have fast storage: both a 16gbit fibrechannel SAN and 10GbE NAS. Caching/storage is definitely not the issue here - we can play back uncompressed 4K in real time.

Audio output is using the onboard/front panel jack on a 2009-2012 Mac Pro. We're just doing a quick audio spot-check to make sure the correct languages are there and in sync so a stereo downmix is perfect. For some reason that works fine on 2.0.1 but not on any newer versions.

I will definitely get you the logs from multiple versions tomorrow (California time). If it helps I could probably also arrange for some sample files and a big donation if we can get this solved. Thanks again.

If the playback quality is not good , try to convert your audios seperately then play them on your VLC.